This invention relates to the alignment and orientation of substrates on a robot which is part of a semiconductor processing system.
The processing of semiconductors often involves multiple process steps such as the deposit of a film on a substrate or substrate by chemical vapor deposition (CVD), the photo etching of the film, as well as heating, cooling and cleaning.
Each of the process operations is generally performed under vacuum in a specialized process chamber. Depending on the nature of each process, either batch processing of semiconductor substrates or individual substrate processing is used. In either of the above systems, for each process step, the process chamber must be vented, the substrate loaded, the chamber sealed and pumped to vacuum. After processing, the steps are reversed.
In batch processing, a cluster of processing chambers are arranged around a substrate transport chamber which is constructed to be kept under vacuum. One or more load lock chambers are connected through slit valves to the transport chamber.
The load locks accommodate cassettes of substrates to be processed. The cassettes are delivered to the load lock by the front end delivery transport of the system. A load lock constructed to accommodate such cassettes is shown in U.S. Pat. No. 5,664,925 owned in common with the subject application. The disclosure of the ""925 patent is incorporated herein by reference, in its entirety.
In batch processing cycling times are reduced, while significantly increasing system throughput. The process and transport chambers are maintained continuously under vacuum, while only the load lock is cycled. The load lock receives the substrates to be processed after being sealed from the transport chamber and vented to atmosphere. The front end port is than sealed and the load lock is pumped to a vacuum consistent with the transport and processing chambers.
A robotic transfer mechanism is mounted within the transport chamber and operates to remove substrates from the load lock and deliver them to the selected process chambers. After processing, the substrates are picked up by the robot and transported to the next process chamber or to a load lock for removal from the transport chamber. In some instances, for timing purposes, these systems may employ buffer stations which are adapted to store substrates either before loading or at other times during the transport of the substrate through the system.
A system of this type is described in U.S. Pat. No. 5,882,413 and an example of a robotic transfer mechanism is shown in U.S. Pat. No. 5,647,724, each of which is assigned to an owner common to this application. The disclosures of these patents are incorporated herein by reference in their entirety.
It has been found that substrates up to 200 mm in diameter can be effectively processed with the cluster type systems. However, there is a trend towards increasing diameters and the cluster systems become unduly large when processing substrates of 300 mm or more in diameter. In some circumstances, there is a need to provide a more compact process handling module, which is capable of being installed in a side by side relation within a small envelope of space. In addition there is a need for system modules which are more adaptable to the wide variety of process chambers and front end delivery transports. A system of this type is described in commonly owned Application for patent Ser. No. 09/897,202 filed Jul. 2, 2001.
In all of the above systems there are requirements for accurate alignment of the substrate on the robot arm of the transport mechanism. This insures that the process is applied in a controllable distribution over the substrate surface. In addition there is a need to orient the substrate in a consistent angular position to insure that each substrate is processed in the same pattern. The orientation step consists of locating an orientation mark, which is generally a notch placed at a predetermined location on the edge of the substrate. The overall registration of the substrate on the robot arm needs to be accomplished at some point accessible to the normal trajectory of the substrate prior to its insertion into a processing chamber.
It is a purpose of this invention to provide a mechanism for accurate and consistent alignment and edge orientation of a substrate on the robot arm.
One of the current solutions to accomplishing this registration function is to provide a separate station for aligning and orienting the substrate prior to placement of the substrate on the robot arm. This complicates the processing path of the substrate with a potential delay in the overall processing cycle time. Another prior art mechanism is constructed at the distal end of the effector. In this system a driven roller is mounted on the distal end with an associated drive motor to rotate the substrate to its desired orientation. This creates a thick profile at the end effector which may obstruct the entrance of the substrate into some process chambers. In addition this weighs down the end effector and makes it cumbersome. Another mechanism is mounted on the robot drive base for engagement by the robot arm. In this configuration, the alignment/orientation mechanism must be moved out of the way of the robot arm prior to movement to a processing chamber.
It is a purpose of this invention to provide alignment of a substrate on a robot arm by mechanically centering the substrate on fixed tip pads and providing a separate orientation module against which the substrate is banked by motion of the effector. This eliminates the need for additional mass on the effector.
The mechanism of this invention consist of an effector constructed with a pair of fixed positioning pads at the its distal end. At the back end of the effector, a pair of idler rollers are mounted for sliding motion along the central longitudinal axis of the effector. The idler rollers are moved by means of a vacuum actuator, into engagement with the inner edge of the substrate and push the substrate into engagement with the positioning pads of the effector. The vacuum actuator has sufficient spring action built in to bias the substrate outward. An edge orientation module is positioned independently and is constructed with a pair of wheels one of which is driven. The substrate is moved into engagement with the wheels in a way that lifts the edge of the substrate free of the positioning pads. The lifting frees the substrate for rotation on the inner idler rollers and the wheels of the orientation module. A simple optical sensor is positioned between the wheels to locate the orientation notch. Once the center of the notch is located, the substrate can be rotated to its specified angular orientation. The lift action may be obtained by the z axis of the robot or by providing a z axis motion for the orientation module.
In an alternate embodiment, the orientation module is mounted on a lower arm of the robot in a position which allows engagement of the substrate edge by movement of the effector. In this instance, it may be advantageous to provide a z axis motion of the orientation module to lift the substrate for rotation. The z axis motion can also be accomplished by mounting the orientation module to the grounded base drive of the robot arm drive and using the z axis supplied as part of the robot drive to allow relative motion between the end effector and the orientation module.